Polyphase watt-hour meter construction



May 27, 1941. w. w. SHERWOOD POLYPHASE WATT-HOUR METER CONS TRUCTION Filed Feb. 10, 1938 2 Sheets-Sheet 1 William m J/zerwood y 1941- w. w. SHERWOOD 43,130

POLYPHASE WATT-HOUR METER CONSTRUCTION Filed Feb. 10, 1938 2 Sheets-Sheet 2 ['Mf? 2"07 (02:73am (d Sherwood Patented May 27, 1941 POLYPHASE WATT-HOUR METER CONS TRUGTION William W. Sherwood, Springfield, 111., assigncr to Sangamo Electric Company, corporation of Illinois Springfield, Ill., 2.

Application February 10, 1938, Serial No. 189,759

3 Claims.

My invention relates, generally, to electric measuring devices, and it has particular relation to polyphase watthour meters. The invention disclosed in this application constitutes an improvement over the construction shown in the cop'ending application of Fred Kurz, SerialNo. 136,337, filed April 12, 1937, and assigned to the assignee of this application, now ent No. 2,129,010.

Accordin to said patent of Kurz, two watthour meter units are provided for applying torque to a single disc. The two watthour meter units are provided for measuring the total energy that has been consumed in a polyphase alternating current circuit. In order to prevent interference between the two watthour meter units which causes errors in registration, a magnetic bridge is provided, which is arranged to bridge the two watthour meter units. This bridge is intended to reduce the interaction between the units which would otherwise take place and thereby substantially reduce the interference between them which results in inaccurate registration. By providing a high permeability path between the two units, it is possible to shield the disc to a large extent from stray magnetic fields which would interact with eddy currents in the disc and cause the interference errors.

It is with a view to further reducing the interference between the two watthour meter elements that this invention is particularly addressed. The magnetic bridging member disclosed in the patent of Kurz is modified to make it more effective and the disc is so constructed that the effect of eddy currents therein in creating interference is reduced materially.

The object of my invention, generally stated, is to provide a polyphase watthour meter of the single disc type that will be simple, efficient, and accurate in operation and which may be readily and economically manufactured.

The principal object of my invention is to reduce the interference between the watthour meter units of a two unit polyphase watthour meter of the single disc type so that the registration of the meter will be substantially unaffected by such interference.

An object of my invention is to improve the coupling between a magnetic bridging member and the cores of the voltage elements of a pair of watthour meter units acting on a single disc.

Another object of my invention is to reduce the flow of eddy currents in a single disc of a two unit watthour meter in sections thereof remote from where they originate.

- the functioning Still another object of my invention is to provide-for obtaining the improved coupling and reduced eddy current flow set forth in the two preceding objects in a single polyphase watthour meter.

Other objects of my invention will, in part, be obvious and, in part, appear hereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shown in the accompanying drawings", and it comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the application of which will be indicatedin the appended claims.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 illustrates, diagrammatically, the construction and connections of a single phase alternatin current watthour meter;

Figure 2 illustrates, diagrammatically, the eddy currents that are generated in the disc by the voltage elements of the single phase watthour meter unit;

Figure 3 illustrates, diagrammatically, the eddy currents that are generated in the disc by the current element of the single phase watthour meter unit;

Figure. 4 illustrates, diagrammatically, the arrangement of two watthour meter units arranged to drive a single disc;

Figure 5 is a view diagrammatically illustrating how one feature of my invention may be applied to the construction shown in Figure 4 for reducing interference between the two watthour meter units;

Figure 6 is a view, in front elevation, of a two unit watthour meter embodying the features of my invention, the cover and register having been omitted in order to more clearly illustrate the in- Vention; V

Figure '7 is a perspective View of the magnetic bridging member employed in practicing my invention; and

Figure 8 is a top plan View of the disc and bridging member with the cores of the watthour meter units being shown by broken lines.

With a View to pointing out the novel features of my invention and the reasons why certain construction details are employed in a two unit single disc meter, reference will first be had to of a watthour meter in which a single watthour meter unit cooperates with a disc to apply torque thereto for measuring the energy that has flowed in a circuit. As shown in Figure 1 of the drawings, the reference character l designates a single phase alternating current circuit, the flow of energy in which is to be measured by a watthour meter that is designated generally at H. The meter H comprises an E-shaped core formed of laminations, on the central leg of which is positioned a voltage coil l3 that is connected across the conductors of the circuit 10. Underneath the core 12 is a c-shaped core N that is also formed of laminations of magnetic material, and it has wound on its legs a pair of current coils 15 through which the current in the conductors of the circuit I0 flows. In the air gap formed between the pole tips 2a, lZb, and I20 of the core l2 and the pole tips Me and Mb of the core M, a disc I6 is rotatably mounted so that a torque is applied thereto which is function of the Voltage across and the current in the circuit [0. A permanent magnet I1 is provided for damping the movement of the disc IS in the usual manner,

In Figure 2 of the drawings by means of the curved lines 20 and the arrow heads thereon I have illustrated the instantaneous direction of the eddy currents in the disc [6 as caused by the flux between the pole tips '29., Ht, and 2c that is generated by the voltage winding l3. These eddy currents react with the flux generated by the current winding I5 in accordance with Lenz law and produce torque for rotating the disc [6.

In a similar marmer in Figure 3 of the drawings, the eddy currents that are generated in the disc l6 by the flux between the pole tips '43. and Nb are indicated by the curved lines 2| with the arrowheads thereon. It will be understood that this representation is for the instantaneous directions of the eddy currents. These eddy currents react age winding l3 for also rotates the disc 16.

It will be observed that the eddy currents represented by the lines 20 and 2| in Figures 2 and 3 are not confined to the region directly underneath the pole tips of the cores l2 and I4 but, rather, that they spread to the remote regions of the disc l6. It will also be observed that the directions of flow of the eddy currents are not circumferential. However, they may be resolved into radial and tangential components. In the regions remote from the cores l2 and I3 there simultaneously exists stray magnetic fields that are generated by the voltage and current windings l3 and i5. These stray magnetic fields may be separated into components that are perpendicular, tangential, and radial with respect to the axis of rotation of the disc IS. The reaction between the perpendicular components of these stray magnetic fields and the radial com ponents of the eddy currents gives rise to forces which apply additional torque to the disc Hi. In a watthour meter in which a single unit is employed and reacts with a single disc, such as shown in Figure 1, these forces go to make up the meter characteristics and, for any particular set of conditions, they can be readily determined.

producing torque which However, when two watthour meter units are arranged to drive a single disc, such as the disc l6, other factors are involved which cannot so readily be determined.

In Figure 4 of the drawings I have illustrated diagrammatically the arrangement of two wattwith the flux generated by the voltunits H and a. for applying torque to a single disc IS. The unit I l is provided with the voltage winding l3 and current winding 15 which may be connected to measure the current and voltage of one phase of a polyphase circuit. The unit la is provided with a voltage winding 13s and a current winding 5a which are arranged to measure the voltage and current of another phase of the polyphase circuit. Even if the units II and a are diametrically opposite and are perfectly symmetrical from a mechanical and electrical standpoint, the torque which is applied for rotating the disc IE will not be the sum of the torques generated by the units II and I la. acting alone. This arises from the fact, as may be seen in Figure 3, that radial components of the eddy currents in the disc l6 represented by the lines 2| and resulting from flux generated by the current winding l5, may interact with flux generated by the voltage winding 13a of the opposite watthour meter unit a. In other words there will be additional torque applied to the disc 16 as the result of interaction between the units l l and I la. In actual practice it is impossible to secure perfect mechanical and electrical symmetry for the two units II and la and, therefore, it is necessary to provide means which will limit to a practical operating minimum the interaction between these two units.

As described in said patent of Kurz, referred to hereinbefore, the interaction between the two units is materially reduced by the provision of an inverted U-shaped bridging member 25 that is shown digrammatically on Figure 5 of the drawings. According to said patent of Kurz, the ends 259. and 25b of the bridging member 25 are turned outwardly and while they are adjacent the upper surface of the disc 16, they are spaced slightly from the adjacent sides of the cores l2 and Ha.

I have found that the interaction between the watthour meter units H and la can be further reduced by providing the ends 25a and 25b of the bridging member 25 with the laterally extending tips 25c and 25d, as shown in Figure 7, which interfit with suitable apertures 26 and 269, which extend through the middle legs of the cores l2 and l2d, as shown in Figure 5. This construction and arrangement of the bridging member 25 provides closer coupling between it and the cores I2 and |2d of the watthour meter units H and a and reduces further the degree of interference and consequent errors in registration between the units II and la. By combining this construction and arrangement of the bridging member 25 with certain changes in the construction of the disc 16 which will presently be described, it is possible to substantially completely eliminate interference between the watthour meter units II and a.

The manner in which the bridging member 25 may be incorporated in a commercial type of polyphase watthour meter is more clearly shown in Figure 6 of the drawings. the polyphase watthour meter is provided with a base 21 on which is mounted a frame member 28 that is formed of non-magnetic material, such as aluminum or an aluminum alloy. The disc I6 is rotatably mounted on the frame member 28 by means of a shaft 29 that is provided with a worm so for driving a register (not shown) that may be mounted on suitable ears or bosses 3| which may be integrally formed with the frame member 28. The bridging member 25 is secured in position on the top of the frame memhour meter As there shown,

ber 28 by any suitable means, such as by the screws 32 that 33 in the flat portion between the vertical branches thereof, as is shown in Figure. 7. An enlarged clearance. hole 3'4 is also provided in this portion to permit adjustment of the upper bearing of the shaft 29; It will be observed that, in this construction, two permanent magnets H are mounted on the frame member 28 and serve to damp the rotation of the disc l6.

While the magnetic bridging member 25, which is preferably formed of high permeability magnetic material such as Mumetal or othersimilar magnetic alloy, can substantially reduce the interaction between the opposite voltage and current coils, it does not reduce the interference between these coils or elements resulting from dissymmetry. This dissymmetry may be due either to mechanical misalignment orto difference in magnetic properties of the magnetic cir-' cuits of the cores of the watthour meter units H and Ha, or to both.

With a view to reducing the interference between the units I! and I In from this cause, the disc I 6 is provided, as shown in Figure 8 of the drawings, with a plurality of radial slots 3'1. It will be noted that the radial slots 31 are in register with the core of the current and voltage elements of the units H and "a. The purpose of the slots 31 is to interrupt the paths for the eddy currents represented by the lines 28 and 2| in Figures 2 and 3 in the regions remote from where they originate. By this means the eddy currents in the disc IS in the region adjacent the unit I [a and generated by the unit II will be reduced to a minimum so that interaction between them and the flux of the unit Ila. will be substantially minimized. The same is true with regard to the eddy currents from the unit a in reacting with the flux from the unit H.

The desired number of slots 31 will, in general, depend upon the arrangement of the units I I and I la with respect to the disc 16. The number should be suincient to reduce the interference to a negligible value without unduly reducing the torque. Furthermore. the number and arrangement should be such as to prevent any pronounced tendency for the disc Hi to lock in certain positions at zero load, with the voltage windings I3 and I 32, only energized. In general, an odd number of slots 31 is desirable, particularly in the embodiment of the invention herein disclosed where the units H and Ha are located on opposite sides of the disc Hi. This arrangement reduces the locking tendency of the disc IE to a point which will enable it to start under loads of less than 1% but does not permit it to creep continuously on the energization only of the voltage windings l3 and I32.-

As the following test data will show, the provision of the bridging member 25 close coupled to the cores of the voltage elements of the watthour meter units ii and a combined with the provision of the radial slots 31 in the disc 16 provides a means for reducing to substantially zero the amount of interference between the two watthour meter units acting on a single disc. These data are obtained by loading one of the watthour meter units, for example the unit H, with a unity power factor load and then applying voltage to the winding 3a or current to the winding of the unit Hg. The current and voltage applied to these windings is shifted in phase with relation to the current and voltage project through clearance holes 5 5a,, is the result ofthe tor bridging member 25 in thewindings unity power factor, are'in phase.

The difference in registration over that obtained by the unit H acting alone when the current or voltage applied to the unit i leis shifted from zero degrees to 180 with respect to the current or voltage applied to the unit M will be designated as A interference. The corresponding difference in registration which results when the current or voltage applied to the unit la is shifted from 96 lag to lead will be called B interference. The A interference, due either to the voltage applied to the winding 13;; or the current flowing through the winding one produced by the interaction of each voltage element l3 or 13s with the diametrically opposite current element 15 or i5a. For the purpose of this description the terms winding and element may be used interchangeably. The B interference is the result of two factors, one being the torque produced by the interaction of the voltage elements 53 and 3a and the other being produced by the interaction of the two current elements l5- and 15s. It will be observed that the A interference is essentially independent of the load, that the B. interference due to interaction of the voltage elements is predominant at light loads, and that the B interference due to the interaction of the current elements is noticeable on heavy loads.

the provision of the bridging member 25 or the radial slots 3! in the disc l6, it was found that the A interference was about 1.8%. Thatis the change in registration caused by the interfering unit was 1.8% of the registration that would have been obtained had the unit, for example the unit I3, alone been energized. The B interference under these conditions was about 0.7%.

Now when the bridging member 25 formed of high permeability magnetic material, such as Mumet-al,

tion of not more than 0.4%. The B interference was not increased but remained at about 0.7%.

In making the foregoing tests without the bridging member 25 but with the disc I 6 provided with the odd number of radial slots 31, the A interference is reduced from 1.8% to about 1.2%. The B interference is reduced from about 0.7% to about 0.4%.

As a final test, the meter was provided with the bridging member 25, and the disc E6 was provided with the radial slots 37. tire range the A interference averaged at zero with a variation of less than 0.2%. The B interference was reduced to less than 0.3%. This test reveals the combined efiectiveness of the and the radial slots 31 and shows that the interference between the two units II and H is reduced thereby to such an extent that the resulting error in registration is negligible.

On polyphase watthour meters that are employed in circuits of large current capacity, the B current interference is particularly noticeable. The construction described herein employing the radial slots 37 registering with the cores of the watthour meter units reduces such interference to a minimum.

It will be obvious that certain changes may l5 and I 3 respectively which, at

tests in a two unit Over the enbe made in the foregoing construction and different embodiments of the invention may be made without departing from the scope thereof. Therefore, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention.

1. In a polyphase induction watthour meter, in combination, non-magnetic frame means, a disc rotatably mounted on said frame means, a pair of induction watthour meter units carried by said frame means and cooperating with said disc for applying torque thereto, said watthour meter units being symmetrically positioned adjacent diametrically opposite edges of said disc and each including a voltage element and a current element disposed on opposite sides of said disc, and a magnetic bridge mem ber carried by said frame means with its ends adjacent said disc and interfitting with the respective cores of the voltage elements of said watthour meter units.

2. In a polyphase induction watthour meter, in combination, non-magnetic frame means, a disc rotatably mounted on said frame means, a pair of induction watthour meter units carried by said frame means and cooperating with said disc for applying torque thereto, said watthour meter units being symmetrically positioned adjacent diametrically opposite edges of said disc and each including a voltage element and a current element disposed on opposite sides of said disc, and a magnetic bridge member carried by said frame means with its ends adjacent said disc and interfitting with the respective cores of the voltage elements of said watthour meter units, there being an odd number of uniformly spaced radial slots in said disc registering with the cores of said voltage and current elements.

3. In a polyphase induction watthour meter, in combination, a rotatably mounted disc, a pair of induction watthour meter units cooperating with said disc for applying torque thereto, said watthour meter units being symmetrically positioned adjacent diametrically opposite edges of said disc and each including a voltage element and a current element with cores individual thereto, and a magnetic bridge member extending between said units with its ends adjacent said disc and interfitting with the respective cores of like elements.

WILLIAM W. SHERWOOD. 

